1. Field of Invention
The present invention relates to a photographing apparatus and a photographing method which allow a flash light photographable range to be kept almost constant in lighting photography (such as a flash light photography), even if a subject is photographed with a zoom lens of which a stop number of brightness (the amount of light which enters a photographing means) of the lens is varied correspondingly to the focal distance of the lens.
2. Description of Related Art
Currently, most of cameras are provided with a flash light as an auxiliary lighting means, so that a subject can be photographed with a flash light in a dark place. Many of cameras having a built-in flash light are provided with an automatic lighting function. Thus, with those cameras, everyone can easily photograph with a flash light.
However, since a flash light is built in the camera body, the amount of emitted light of the flash light is limited. In addition, the maximum emitted light amount, which is the so-called guide number (hereinafter abbreviated as GN) value, depends on the camera. The emitted light amount of the flash light is proportional to the GN value.
Flash light systems of most cameras have a light adjusting function. When the distance between a camera and a subject, namely, a focal distance, is in a flash light photographable range, the light adjusting function automatically adjusts the emitted light amount of the flash light so that the subject can be correctly exposed.
However, as the focal distance is apart from the flash light photographable range, the subject is gradually under-exposed, even with the maximum emitted light amount of the flash light.
When a camera is provided with a zoom lens of which the brightness (F number) of the lens is varied corresponding to the focal distance (namely, the F number of the lens is dropped (hereinafter, referred to as F drop)), the distance of which the subject is under-exposed at the focal distance (for example, wide end) of the brightest open F number is different from the distance of which the subject is under-exposed at the focal point (for example, tele end). As the F drop of the zoom lens is larger, the distance in which the subject is under-exposed becomes larger. When the subject is zoomed, the flash light photographable range is varied largely.
To solve such a problem, Japanese Patent Laid-Open Publication No. SHO 56-17577 discloses an invention in which when a zoom magnification becomes large, the diaphragm is not open with the minimum stop number F which is necessary for obtaining a predetermined depth of field.
In addition, Japanese Patent Laid-Open Publication No. SHO 60-3571.7 discloses an invention in which a driving portion is disposed at a member that is moved by a zooming operation, a cam portion is disposed at an operating portion to which a diaphragm lever with which a stop-down operation is performed is rotatably disposed, the driving portion and the cam portion are engaged when the driving portion is moved by the zooming operation, and the operating member is driven and thereby the diaphragm lever is deformed, so the fluctuation of the stop number due to the zooming operation can be compensated.
In addition, a technology of which the distance to a subject is measured and the effective sensitivity of an image pickup device is increased corresponding to the distance is known. In addition, Japanese Patent Laid-Open Publication No. 2000-162679 describes an invention in which auxiliary lighting compensates the insufficiency of the emitted light amount of main lighting so as to increase the effective sensitivity of the image pickup device.
However, since the relation between the focal distance and the exposure is not considered in flash light photography, when the zooming operation is performed, an F drop takes place. As a result, the brightness of the lens is varied. The emitted light amount of the flash light for correctly exposing the subject cannot be obtained depending on the focal distance. Thus, even if the subject is photographed with a zoom lens of which the brightness of the lens is varied depending on the focal distance, the flash light photographable range is varied largely.
Therefore, an object of the present invention is to provide a photographing apparatus and a photographing method which allow a flash light photographable range to be kept almost constant even if the brightness of a lens is varied due to an F drop when a zooming operation is performed.